Technical Field
Embodiments of the invention relate generally to superconducting magnets and, more specifically, to a system and method for imaging four-dimensional flow of a fluid within a volume of an imaged subject.
Discussion of Art
Magnetic resonance imaging (“MRI”) is a widely accepted and commercially available technique for obtaining digitized visual images representing the internal structure of objects having substantial populations of atomic nuclei that are susceptible to nuclear magnetic resonance (“NMR”). Many MRI systems use superconductive magnets to impose a strong main magnetic field on the nuclei in the object to be imaged. The nuclei are excited by a radio frequency (“RF”) signal at characteristics NMR (Larmor) frequencies. By spatially disturbing localized magnetic fields surrounding the object and analyzing the resulting RF responses from the nuclei as the excited protons relax back to their lower energy normal state, a map or image of these nuclei responses as a function of their spatial location is generated and displayed. An image of the nuclei responses provides a non-invasive view of an object's internal structure.
Some MRI systems can obtain four-dimensional (“4D”) images used in volumetric assessment of hemodynamic-related cardiovascular pathologies, i.e., 4D imaging of blood flowing through a region on interest (“ROI”) within a patient vessel. Such MRI systems, sometimes also referred to as “Three-Dimensional Phase-Contrast MRI systems”, presently use whole-volume acquisition over the ROI. Whole-volume acquisition, however, often saturates the nuclei of imaged blood, which results in a low signal to noise ratio (“SNR”), and typically yields images having low accuracy in flow measurements. Additionally, MRI systems that use free-breathing acquisition in combination with whole-volume acquisition for 4D imaging are highly susceptible to residual motion artifacts. Accordingly, many MRI systems used to obtain 4D images require the use of a contrast agent. The use of a contrast agent, however, may prove problematic for certain procedures performed after injection of the contrast agent, e.g., MRA, perfusion, and LGE, and/or for patients suffering from renal insufficiencies. Moreover, certain countries disfavor the use of contrast agents.
What is needed, therefore, is a system and method for imaging 4D flow of a fluid within a volume of an imaged subject that does not require the use of a contrast agent.